1. Field of the Invention
The present invention relates to canisters that can be used in fuel vapor processing apparatus which process fuel vapor produced in internal combustion engines of automobiles.
2. Description of the Related Art
A known canister is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2002-266709. Referring to FIG. 14, there is shown a canister 101 disclosed in this publication.
As shown in FIG. 14, the canister 101 includes a case 102, a main adsorption material 113 and an auxiliary adsorption material 114 disposed within the case 102. A main chamber (including a first chamber 121 and a second chamber 122) and an auxiliary chamber 123 communicating with the main chamber (i.e., the first chamber 121 and the second chamber 122) and also communicating with the atmosphere are defined within the case 102. The main adsorption material 113 is filled within the main chamber (i.e., the first chamber 121 and the second chamber 122) for adsorbing a fuel component contained in a mixture of air and vaporized fuel introduced into the main chamber from a fuel tank (not shown). A mixture of air and vaporized fuel (fuel vapor) will be hereinafter called a “fuel vapor containing gas.” The auxiliary adsorption material 113 is filled within the auxiliary chamber 123 and can adsorb a part of the fuel component (fuel vapor) contained in the fuel vapor containing gas introduced from the main chamber (i.e., the first chamber 121 and the second chamber 122) before the part of the fuel component is discharged from the auxiliary chamber 123 to the atmosphere. The resistance against flow of the fuel vapor containing gas through the auxiliary chamber 123 filled with the auxiliary adsorption material 114 is set to be smaller than the resistance against flow of the gas through the main chamber (i.e., the first chamber 121 and the second chamber 122) filled with the main adsorption material 113.
With the known canister 101, the fuel vapor produced in the fuel tank is introduced into the main chamber (i.e., the first chamber 121 and the second chamber 122) and is thereafter introduced into the auxiliary chamber 123 before being discharged to the atmosphere. Therefore, the main adsorption material 113 and the auxiliary adsorption material 114 adsorb the fuel vapor (i.e., the fuel component) of the fuel vapor containing gas before the gas is discharged to the atmosphere. Because the resistance against flow of the fuel vapor containing gas through the auxiliary chamber 123 filled with the auxiliary adsorption material 114 is set to be smaller than the resistance against flow of the gas through the main chamber (i.e., the first chamber 121 and the second chamber 122) filled with the main adsorption material 113, it is possible to suppress increase of resistance against flow of the gas (i.e., the fuel vapor containing gas) through the main chamber (i.e., the first chamber 121 and the second chamber 122) and the auxiliary chamber 123 during filling of fuel into the fuel tank. Therefore, the fuel filling operation can be facilitated.
In the known canister 101, activated carbon is used as the main adsorption material 113 of the main chamber (i.e., the first chamber 121 and the second chamber 122). On the other hand, a ceramic adsorption material having a honeycomb or slit structure or an adsorption sheet including partition walls constituting a honeycomb structure or a slit structure is used as the auxiliary adsorption material 114. Here, each of the partition walls includes two gas permeable sheets and activated carbon that is held between the sheets so as to be integrated therewith. Alternatively, each of the partition walls includes a single gas permeable sheet and activate carbon adhered to opposite sides of the sheet.
In this way, a ceramic adsorption material having a honeycomb or slit structure or an adsorption sheet including partition walls that constitute a honeycomb or slit structure is used as the auxiliary adsorption material 114. Therefore, the construction of the canister 101 is complicated and increase of the manufacturing cost is inevitable.
Therefore, there is a need in the art for a canister that can facilitate the fuel filling operation without accompanying substantial increase of the manufacturing cost.